There is known a vehicle provided with a continuously variable transmission of a mechanical type or an electric type. Examples of the mechanical type continuously variable transmission include: a belt-and-pulley type continuously variable transmission wherein a pair of variable-diameter pulleys effective diameters of which are continuously variable are connected to each other by a transmission belt; and a traction type continuously variable transmission in which a disc is supported between two annular U-grooves formed in opposite surfaces of a pair of cones such that the disc is rotatable about an axis which is pivotable in a plane including axes of rotation of the cones. One example of the electric type continuously variable transmission has a differential gear device including a first rotary element connected to an engine, a second rotary element connected to an electric motor to generate a reaction force corresponding to an output of the engine, and a third rotary element which outputs a vehicle drive force.
In the vehicle provided with such a continuously variable transmission as described above, the output torque of a vehicle drive power source and the speed ratio of the continuously variable transmission are controlled such that the operating state of the vehicle drive power source follows a highest fuel economy line, so that the vehicle can exhibit not only a high degree of fuel economy but also a high degree of drivability. However, controlling the output torque of the vehicle drive power source and the speed ratio of the continuously variable transmission so as to ensure the high degree of fuel economy tend to restrict a target vehicle drive force and the operating speed of the vehicle drive power source with respect to an actual amount of operation of a vehicle accelerating member (e.g., an accelerator pedal) by an operator of the vehicle to accelerate the vehicle, giving rise to a problem of an insufficient degree of acceleration of the vehicle as felt by the vehicle operator.
In view of the problem described above, it has been proposed to temporarily increase the target vehicle drive force, and raise the target rotating speed of an input shaft of the continuously variable transmission, namely, the operating speed of the vehicle drive power source, with respect to an actual amount of operation of the vehicle accelerating member by the vehicle operator to accelerate the vehicle, to ensure a sufficient degree of acceleration of the vehicle as felt by the vehicle operator. For example, Patent Literature 1 proposes a control apparatus configured to control the vehicle provided with a continuously variable transmission, as described above. However, this control technique to improve the acceleration performance of the vehicle as described above suffers from another problem of generation of an initial acceleration shock upon an operation of the vehicle accelerating member to accelerate the vehicle.
On the other hand, Patent Literature 2 proposes a control technique to mitigate initial acceleration and deceleration shocks of the vehicle upon operations of the vehicle accelerating member to accelerate and decelerate the vehicle, by performing a smoothing operation with a second-order delay filter in the form of a filtering portion at a predetermined smoothing ratio, with respect to initial rates of increase and decrease of the actual amount of operation of the vehicle accelerating member by the vehicle operator to accelerate and decelerate the vehicle.